The chalk mark is the actual location of the bullet entrance on Kennedy's jacket.
The bullet trajectory in both photos is represented by the rod, and we can see the angle Specter uses is equal to the angle from the 6th floor to the Limo, as calculated by the surveyors theodolite in the background.
Since they couldn't skewer the Kennedy stand-in, they duplicated the trajectory in 2D mapped onto the 3D wound locations.
The straight line at the same angle from the 6th floor, between Kennedy's neck wound through to Connally's back wound completely validates the SBF!
And finally, since we know Kennedy's jacket was bunched, the chalk mark has to be in a lower location on an unbunched jacket.


JohnM
Thank you John but that doesn't comport with the WC testimonies of Secret Service agent Thomas Kelley and FBI Agent Lyndal Shaneyfelt.
Mr. SPECTER. What marking, if any, was placed on the back of President Kennedy--the stand-in for President Kennedy?
Mr. KELLEY. There was a chalk mark placed on his coat, in this area here.
Mr. SPECTER. And what did that chalk mark represent?
Mr. KELLEY. That represented the entry point of the shot which wounded the President.
Mr. SPECTER. And how was the location for that mark fixed or determined?
Mr. KELLEY. That was fixed from the photographs of a medical drawing that was made by the physicians and the people at Parkland and an examination of the coat which the President was wearing at the time.
Mr. SPECTER. As to the drawing, was that not the drawing made by the autopsy surgeons from Bethesda Naval Hospital?
Mr. KELLEY. Bethesda Naval.
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Mr. SHANEYFELT. All of the photographs made through the rifle sight that are shown on the exhibit in the lower left-hand corner were sighted on the spot that was simulating the spot where the President was wounded in the neck. The chalk mark is on the back of the coat.